Soil Nitrogen and Carbon Dynamics in a Prairie Soil - a Century Perspective.

The soil organic matter content of soil, a critical indicator of soil health, often changes slowly, so that the influence of management practices can be ascertained only in long-term experiments spanning many decades. The historical dryland plots at Lethbridge, Alberta, established in 1911, offer a unique opportunity to study these responses because they were established shortly after the lands was initially cultivated, and because their originators had the foresight to archive soils dating back to 1910. Our objective is to describe the changes in soil nitrogen and carbon concentration in the surface soil, from 1910 through 2011, based on a comprehensive re-analysis of archived samples. The results demonstrate significant losses of carbon and nitrogen in early decades after cultivation, and then a levelling off, at levels depending on crop rotation and fertilizer amendment. Current soil nitrogen and carbon concentrations reflect long-term inputs from crop residues, as influenced by cropping intensity and fertilizer regime. The study also demonstrates significant inputs of non-fertilizer nitrogen, presumably from atmospheric sources.  These findings provide insights into ways of maintaining soil health, and provide a unique data set for evaluating soil carbon and nitrogen models.